•The role of Al2O3 inclusions in the pitting corrosion initiation stage in a marine environment was studied.•A high dislocation density region existed around Al2O3 inclusions in the cold rolling ...Q460NH steel.•A mechanism different from the galvanic coupling was used to explain the selective dissolution of matrix around inclusions.•Al2O3 clusters had a more negative effect on the corrosion behaviour of the Q460NH steel analysed than single inclusions.
The influence of Al2O3 inclusions on the localized corrosion behaviour of Q460NH steel was investigated in a simulated marine environment. According to the current sensing atomic force microscopy (CS-AFM) result, there was no galvanic couple between Al2O3 inclusions and the adjacent steel. Therefore, a different mechanism from that traditionally used (considering the galvanic coupling between inclusions and matrix) to explain the selective dissolution of the matrix around inclusions, dominated the pit initiation and propagation process in this system. Electron backscattered diffraction (EBSD) analysis showed a region of high dislocation density around the inclusions. Both microcrevices and the high dislocation density region around inclusions can easily induce localized corrosion. The catalytic-occluded cells and oxygen-concentration cell could accelerate the propagation of the pits. Furthermore, inclusion clusters had a larger negative effect than single inclusions on the corrosion resistance of the steel. Scanning vibrating electrode technique (SVET) measurements confirmed that inclusions play a key role in the corrosion process.
Slow strain rate tensile tests, combined with fracture morphology observation and electrochemical measurements, were conducted to investigate the SCC behavior of E690 steel in simulated seawater at ...open circuit potential (OCP) and various cathodic potentials. Results showed that E690 steel had a certain degree of SCC susceptibility at OCP in simulated seawater and had a high susceptibility to hydrogen embrittlement (HE) at high cathodic potentials. The SCC susceptibility showed a distinct decline at −850mVSCE because of the inhibition of the anodic dissolution, and the fracture surface exhibited a ductile failure of dimple. The SCC susceptibility presented a remarkable increase at −950mVSCE with a distinct feature of brittle rupture and increased drastically as the potential became more negative. The bainitic lath boundaries had an opposite effect on the SCC behaviors of E690 steel. The fracture modes at OCP and various cathodic potentials were all transgranular cracking.
Flavonoids from plants are particularly important in our diet. Buckwheat is a special crop that is rich in flavonoids. In this study, four important buckwheat varieties, including one tartary ...buckwheat and three common buckwheat varieties, were selected as experimental materials. The total flavonoid content of leaves from red-flowered common buckwheat was the highest, followed by tartary buckwheat leaves. A total of 182 flavonoid metabolites (including 53 flavone, 37 flavonol, 32 flavone C-glycosides, 24 flavanone, 18 anthocyanins, 7 isoflavone, 6 flavonolignan, and 5 proanthocyanidins) were identified based on Ultra Performance Liquid Chromatography-Electrospray Ionization-Tandem Mass Spectrometry (UPLC-ESI-MS/MS) system. Through clustering analysis, principal component analysis (PCA), and orthogonal signal correction and partial least squares-discriminant analysis (OPLS-DA), different samples were clearly separated. Considerable differences were observed in the flavonoid metabolites between tartary buckwheat leaves and common buckwheat leaves, and both displayed unique metabolites with important biological functions. This study provides new insights into the differences of flavonoid metabolites between tartary buckwheat and common buckwheat leaves and provides theoretical basis for the sufficient utilization of buckwheat.
High strength low alloy steels are extensively applied in marine engineering structures (cross-sea bridge, ocean platform, etc), which are usually subjected to severe corrosion in marine atmosphere. ...In this work, the corrosion behaviors of 550 MPa-grade high strength low alloy marine steels with varied Si content were studied in simulated marine atmosphere. Results show the increase of Si could significantly facilitate the formation of α-FeOOH and enrichment of Cr and Cu in inner rust layer, making the rust layer compact and cation-selective. Si and Cr can be co-enriched in inner rust layer to form mixed or complex oxides with amorphous network structure, which could greatly improve the compactness and stability of rust layer and thereby enhance the corrosion resistance of low alloy steel.
A correlative method based on TEM, EBSD, and SKPFM was used to investigate the corrosion fatigue behaviors of E690 steel in simulated marine atmosphere. Results revealed E690 steel is susceptible to ...corrosion fatigue cracking in this environment and PAGBs play a vital role in crack initiation and propagation. Intergranular microcracks were prone to initiate along PAGBs probably due to high-angle grain boundaries and micro-galvanic effect between martensite-austenite (M-A) constitutes and adjacent ferrite. Segregation of alloy elements within M-A constitutes introduced Volta potential variation between M-A constitutes and adjacent ferrite, resulting in micro-galvanic corrosion between them and eventually intergranular crack initiation along PAGBs.
•Corrosion pits were more likely to form in the coastal–industrial environment with Cl- ions concentrating at the bottom of pits.•The mechanical property and residual corrosion fatigue life of ...corroded Q690qE steel was significantly reduced with increase in pre-corrosion time.•A prediction model for the residual corrosion fatigue life of corroded Q690qE steel was developed.•The corrosion fatigue initiation mechanism of pre-corroded steel was proposed.
The corrosion behavior of Q690qE high-strength bridge steel in simulated coastal–industrial environment was investigated through accelerated corrosion, and the corrosion features under different corrosion times were characterized. The effect of pre-corrosion level on mechanical and corrosion fatigue behaviors was also studied by using pre-corroded fatigue samples. Results show that corrosion pits were more likely to form in this environment, with chloride ions concentrating at the bottom of the pits, resulting in significant loss of the mechanical property and corrosion fatigue life. The corrosion fatigue initiation mechanism was proposed, and a prediction model for the residual corrosion fatigue life of corroded Q690qE steel was developed.
•The local chemistry-electrochemistry underneath disbonded coating were investigated.•A considerably low pH and remarkable concentration of Cl− were observed at the bottom of disbonded coating.•The ...simulated solutions in the crevice were established and SCC susceptibility was evaluated.
In this study, local chemical and electrochemical states underneath disbonded coatings were investigated using a simulated system. Moreover, the stress corrosion cracking (SCC) susceptibility of X80 steel at different positions was evaluated. Results demonstrated that the microenvironment underneath the disbonded coating changed considerably under cathodic protection (CP). The dissolved oxygen content dropped quickly and transformed into anaerobic state immediately. The pH at the bottom of disbonded coating evolved into an acidity of ~5, accompanied by a remarkable concentration of Cl−, which were probably responsible for the severe corrosion and high SCC susceptibility at the crevice bottom. By contrast, the middle part of the disbonded coating had low SCC susceptibility because of effective CP and weak hydrogen evolution.
The mechanical and corrosion fatigue properties of Q690 bridge steels produced by two different process were comparatively investigated. The steel produced by thermal-mechanical controlled processing ...(TMCP) and tempering had a slightly superior corrosion fatigue property to that produced by intercritical quenching & tempering (IQT). However, the TMCP + T prepared steel had a poor ductility and corrosion fatigue microcracks were prone to initiate due to high density of dislocations and M/A constituents. On the contrary, the steel produced by IQT had a good combination of mechanical and corrosion fatigue property. The corrosion fatigue initiation and propagation mechanism for both steels was proposed.
Simulated microstructures of the typical CGHAZ, FGHAZ, and ICHAZ of an E690 welded joint were prepared with heat treatment at peak temperatures of 1300, 850, and 750°C, respectively. Slow strain rate ...tensile (SSRT) tests were implemented to investigate the stress corrosion cracking (SCC) behavior of E690 steel and the simulated HAZ microstructures in a SO2-polluted marine atmosphere. Results revealed that E690 steel and its simulated HAZ microstructures all had a high SCC susceptibility in the simulated SO2-polluted marine atmosphere with a combined mechanism of AD and HE. The SCC susceptibility gradually increased in the following order: BM, CGHAZ, FGHAZ, and ICHAZ. The cracking mode of BM and CGHAZ was transgranular, whereas that of FGHAZ and ICHAZ was intergranular. The lower SCC susceptibility of BM and CGHAZ was probably due to the impeding effect of lath bainitic grain boundaries on SCC propagation, whereas the higher SCC susceptibility of FGHAZ and ICHAZ was attributed to the facilitating effect of M-A islands on crack initiation and propagation.
An equiatomic FeCoCrNi high entropy alloy (HEA) with high strength and excellent hydrogen embrittlement (HE) resistance is manufactured by the precipitation of nano-sized NbC during thermo-mechanical ...processing. NbC precipitates make the HEA obtain extraordinary mechanical properties via pinning dislocations. With the precipitation strengthening also comes the grain refinement strengthening. Furthermore, the coherent/semi-coherent NbC interfaces are regarded as reversible hydrogen traps based on thermal desorption analysis, thereby increasing the tolerance of HEA to dissolved hydrogen. Despite owning higher strength than the unreinforced one, the precipitation strengthened HEA still manifests superior HE resistance due to NbC preventing hydrogen transport by dislocations.
•Nano-sized NbC dispersed in matrix via TMP can strengthen the HEA effectively.•H bonding strengths are in the order of grain boundary> interstitial site> NbC.•NbC prevents hydrogen transport by mobile dislocations to grain boundary.•NbC strengthened HEA has lower HE susceptibility than the unreinforced one.
PDF
